Grinding wheel

ABSTRACT

A grinding wheel for grinding a workpiece containing a ductile material, the grinding wheel including an annular wheel base having a fixed end adapted to be fixed to a lower end of a spindle and having a free end adapted to face the workpiece to be ground, and a plurality of grindstones each shaped as a rectangular plate, disposed on the free end of the annular wheel base, and arrayed at predetermined intervals with respective longer sides disposed along circumferential directions of the wheel base. Each of the grindstones includes an electroformed grindstone shaped as a rectangular plate and made up of abrasive grains secured together by nickel plating, and has a thickness of 1 mm or smaller and a value ranging from 5 inclusive to 35 exclusive that is represented by a ratio of a height from the free end to the thickness.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a grinding wheel.

Description of the Related Art

There has been known a technology in which substrates made of silicon, gallium arsenide, ceramic, glass, and so on and supporting semiconductor devices formed thereon are ground using a grinding wheel including an annular array of grindstones disposed on a wheel base (see, for example, Japanese Patent No. 4885376).

SUMMARY OF THE INVENTION

According to Japanese Patent No. 4885376, each of the grindstones on the grinding wheel includes a segment shaped as a rectangular plate that is made of abrasive grains of diamond secured together by a bond. The grindstones are fixed to the lower surface, i.e., free end, of the wheel base for grinding a workpiece. The bond included in the grindstones is selected from a resin bond, a metal bond, and a vitrified bond. The segments of the grindstones have a thickness and height (amount of protrusion) set to such values that they will not crack while grinding a workpiece. Specifically, the thickness is in the range of approximately 2 to 4 mm, and the height is in the range of approximately 4 to 5 mm. When resin-packaged substrates that include encapsulated semiconductor device chips, for example, are ground by an existing grinding wheel, ductile materials such as resin or metal contained in the substrates tend to be extended into burrs partly due to requirements for thinned wafer-level packages.

It is therefore an object of the present invention to provide a grinding wheel that is more capable of preventing ductile materials contained in workpieces, such as resin or metal, from being extended into burrs than existing grinding wheels.

In accordance with an aspect of the present invention, there is provided a grinding wheel for grinding a workpiece containing a ductile material, the grinding wheel including an annular wheel base having a fixed end adapted to be fixed to a lower end of a spindle and having a free end adapted to face the workpiece to be ground, and a plurality of grindstones each shaped as a rectangular plate, disposed on the free end of the annular wheel base, and arrayed at predetermined intervals with respective longer sides disposed along circumferential directions of the wheel base. Each of the grindstones includes an electroformed grindstone shaped as a rectangular plate and made up of abrasive grains secured together by nickel plating, and has a thickness of 1 mm or smaller and a value ranging from 5 inclusive to 35 exclusive that is represented by a ratio of a height from the free end to the thickness.

Preferably, the thickness of each of the rectangular, plate-shaped grindstones is 0.5 mm or smaller. Preferably, the workpiece contains resin or metal as the ductile material on a surface thereof to be ground by the grinding wheel.

According to the present invention, the grinding wheel is more capable of preventing ductile materials contained in workpieces, such as resin or metal, from being extended into burrs than existing grinding wheels.

The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a bottom view illustrating a configuration example of a grinding wheel according to an embodiment of the present invention;

FIG. 2 is a cross-sectional view of the grinding wheel taken along line (II)-(II) of FIG. 1; and

FIG. 3 is a fragmentary cross-sectional view of a grinding apparatus incorporating the grinding wheel illustrated in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of the present invention will be described in detail hereinbelow with reference to the accompanying drawings. The present invention is not limited to the details of the embodiment described below. The components described below cover those which could easily be anticipated by those skilled in the art and those which are essentially identical to those described above. Further, the arrangements described below can be combined in appropriate manners. Various omissions, replacements, or changes of the arrangements may be made without departing from the scope of the present invention.

A grinding wheel according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a bottom view illustrating a configuration example of the grinding wheel, denoted by 1, according to the present embodiment. FIG. 2 is a cross-sectional view of the grinding wheel 1 taken along line (II)-(II) of FIG. 1. FIG. 3 is a fragmentary cross-sectional view of a grinding apparatus 100 incorporating the grinding wheel 1 illustrated in FIG. 1. As illustrated in FIGS. 1 and 2, the grinding wheel 1 according to the present embodiment includes an annular wheel base 10 and a plurality of grindstones 20.

As illustrated in FIG. 3, the grinding apparatus 100 includes a spindle 120 extending vertically and having a lower end 121 with a wheel mount 122 secured thereto. The spindle 120 is rotatable about its central axis by a rotary actuator, not illustrated. The grinding wheel 1 is fixed to the wheel mount 122 and rotatable about a rotational axis 2 thereof by the spindle 120. The grinding apparatus 100 also includes a chuck table 110 disposed in facing relation to the lower end 121 of the spindle 120 along the rotational axis 2. The chuck table 110 has a holding surface 111 for holding a workpiece 200 (see FIG. 3) under suction thereon. The chuck table 110 is rotatable about its rotational axis 112 perpendicular to the holding surface 111 by a rotary actuator, not illustrated. The rotational axis 2 of the grinding wheel 1 is aligned with the central axis of the annular wheel base 10.

According to the present embodiment, the workpiece 200 illustrated in FIG. 3, which is a target to be ground by the grinding wheel 1, contains a ductile material disposed on a surface 201 of the workpiece 200 that is to be ground. According to the present embodiment, the ductile material includes metal or resin. The workpiece 200 may be in the form of a circular or rectangular packaged substrate having a plurality of resin-encapsulated devices, a resin plate, a metal plate, or a composite substrate containing metal and resin. According to the present invention, however, the workpiece 200 is not limited to such details, but may be a semiconductor wafer or optical device wafer in the form of a circular plate made of a base material such as silicon, sapphire, silicon carbide (SiC), or gallium arsenide, with a film of ductile material such as a resin film or a metal film formed on the surface 201 to be ground.

As illustrated in FIGS. 1 and 2, the wheel base 10 has a circular through hole 11 defined centrally therein and extending therethrough along the rotational axis 2. As illustrated in FIG. 3, the wheel base 10 has a fixed end 12 providing a surface lying perpendicularly to the rotational axis 2 and fixed to the lower end 121 of the spindle 120 and a free end 13, opposite the fixed end 12, providing another lying perpendicularly to the rotational axis 2 and facing the surface 201 of the workpiece 200 that is to be ground by the grinding wheel 1 when the grinding wheel 1 is mounted in the grinding apparatus 100. According to the present embodiment, the through hole 11 is radially defined by a tapered surface inclined such that the diameter of the through hole 11 is progressively larger toward the free end 13. However, according to the present invention, the through hole 11 is not limited to such a shape, but may not be radially defined by a tapered surface. According to the present embodiment, the wheel base 10 is made of metal such as stainless steel, for example.

As illustrated in FIGS. 1 and 2, the wheel base 10 has an annular slot 14 defined in an outer circumferential edge portion of the free end 13 and having a width large enough to have a plurality of grindstones 20 fitted therein. Therefore, the width of the annular slot 14 is determined depending on the thickness, denoted by 23, of the grindstones 20. According to the present embodiment, the annular slot 14 has a depth along the rotational axis 2 of the grinding wheel 1, i.e., along the thickness of the wheel base 10. In the embodiment illustrated in FIG. 1, the annular slot 14 extends continuously fully circumferentially along the outer circumferential edge portion of the free end 13, and the depth of the annular slot 14 is uniform fully circumferentially along the outer circumferential edge portion of the free end 13. However, according to the present invention, the annular slot 14 is not limited such details. Alternatively, the wheel base 10 may have a series of discrete slots defined in the outer circumferential edge portion of the free end 13 and having respective circumferential lengths corresponding to respective lengths 21 of the longer sides of the grindstones 20, the discrete slots being spaced apart by intervals 22 in the circumferential directions.

As illustrated in FIGS. 1 and 2, the wheel base 10 has a plurality of grinding fluid supply channels 15 defined therein radially inwardly of the annular slot 14 and extending therethrough along the rotational axis 2. According to the present embodiment, the grinding fluid supply channels 15 have openings facing the free end 13 that are defined in the tapered surface that radially defines the through hole 11. However, according to the present invention, the openings of the grinding fluid supply channels 15 that face the free end 13 are not limited to such details, but may be defined in the free end 13 radially outwardly of the tapered surface that radially defines the through hole 11. According to the present embodiment illustrated in FIG. 1, the grinding fluid supply channels 15 include six grinding fluid supply channels spaced apart at constant intervals in the circumferential directions. When the grinding wheel 1 is mounted in the grinding apparatus 100, the openings of the grinding fluid supply channels 15 that face the fixed end 12 are connected to a predetermined grinding fluid supply source. The grinding fluid supply source supplies a grinding fluid 126 through the openings of the grinding fluid supply channels 15 that face the fixed end 12 and the openings of the grinding fluid supply channels 15 that face the free end 13 to an area of the surface 201 of the workpiece 200 that faces along the rotational axis 2 an area of the grinding wheel 1 that lies radially inwardly of the grindstones 20. The grinding fluid 126 includes water or pure water, for example. Another grinding fluid supply source 125 supplies the grinding fluid 126 to an area of the surface 201 of the workpiece 200 that faces along the rotational axis 2 an area of the grinding wheel 1 that lies radially outwardly of the grindstones 20.

As illustrated in FIGS. 1 and 2, the wheel base 10 has a plurality of internally threaded mounting screw holes 16 defined in an outer circumferential edge portion of the fixed end 12 thereof. According to the present embodiment illustrated in FIG. 1, the mounting screw holes 16 include six mounting screw holes spaced apart at constant intervals in the circumferential directions. Each of the mounting screw holes 16 is located at a position radially aligned with an intermediate position between adjacent two of the grinding fluid supply channels 15 along the circumferential directions. As illustrated in FIG. 3, a plurality of screws 124 are threaded through respective mounting holes 123 defined in the wheel mount 122 into the respective mounting screw holes 16 and tightened to fasten the grinding wheel 1 to the lower end 121 of the spindle 120.

The grindstones 20, each shaped as a rectangular plate, have their longer sides, which have the respective lengths 21, oriented along the circumference directions of the wheel base 10 and are arrayed and spaced apart at the intervals 22 in the circumferential directions. The grindstones 20 have shorter sides oriented along the rotational axis 2, i.e., along the depthwise directions of the annular slot 14, and have their thickness 23 oriented radially of the wheel base 10. The grindstones 20 are inserted and fitted in the annular slot 14 and fixed to the free end 13 of the wheel base 10 by an adhesive for use with metal or the like. The grindstones 20 as they are fixed to the free end 13 have portions protruding from the free end 13 along the rotational axis 2 of the grinding wheel 1, i.e., along the thicknesswise directions of the wheel base 10. According to the present embodiment, the grindstones 20 have their longer sides curved along the circumferential curvature of the annular slot 14 and are snugly inserted and fitted in the annular slot 14. However, the present invention is not limited to such details. Rather, the grindstones 20 may have their longer sides not curved, but oriented tangentially to the circumference of the wheel base 10, and may be forcibly fitted in the annular slot 14 and fixed to the wheel base 10.

Each of the grindstones 20 includes an electroformed grindstone shaped as a rectangular plate and made up of abrasive grains of diamond, cubic boron nitride (CBN), or the like that are secured together by an electroformed bond including nickel plating. The thickness 23 of each of the grindstones 20 is 1 mm or smaller, preferably 0.5 mm or smaller. The aspect ratio of each of the grindstones 20, i.e., represented by the value of the ratio of the height (amount of protrusion) 24 protruding from the free end 13 of the wheel base 10 to the thickness 23 is in the range of 5 inclusive to 35 exclusive. The grindstones 20 as they are fitted in the annular slot 14 have end faces remote from their portions in the annular slot 14, and the end faces act as grinding faces 25 for grinding the surface 201 of the workpiece 200 on the chuck table 110 in abrasive contact therewith. The grinding faces 25 of the grindstones 20 have a radial length as the thickness 23 and a circumferential length as the length 21 of the longer side, and are of a circumferentially slender shape.

The abrasive grains included in the grindstones 20 have a central grain diameter ranging from 4 to 30 μm. The granularity, as converted from the central grain diameter, of the abrasive grains included in the grindstones 20 ranges from #360 to #2500. The magnitude of the granularity of grindstones is defined by JIS “R6001: The granularity of abrasive materials for grindstones” and represents a parameter whose number decreases as the central grain diameter becomes larger and increases as the central grain diameter becomes smaller.

The grindstones 20 are produced and assembled as follows: An electroformed grindstone shaped as a large plate having a predetermined thickness 23 is formed and then cut into a plurality of rectangular segments by a wire electric discharge process. Each of the grindstones 20 cut from the electroformed grindstone has a thickness 23 of 0.5 mm, a longer-side length 21 of 15 mm, and a shorter-side length (height) of 5 mm, for example. The grindstones 20 are inserted and fitted in the annular slot 14 that is 1 mm deep at spaced intervals 22 of several millimeters, and fixed to the free end 13 of the wheel base 10 at a height 24 of 4 mm, with an aspect ratio of 8.

Operation of the grinding apparatus 100 that incorporates the grinding wheel 1 according to the present embodiment will be described below with reference to the drawings. The screws 124 are threaded through the respective mounting holes 123 in the wheel mount 122 into the respective mounting screw holes 16 and tightened to fasten the grinding wheel 1 to the lower end 121 of the spindle 120. Then, the workpiece 200 placed on the holding surface 111 of the chuck table 110 and held under suction on the holding surface 111 with the surface 201 facing the grinding wheel 1.

As illustrated in FIG. 3, the chuck table 110 is rotated about the rotational axis 112 by the rotary actuator thereof, rotating the workpiece 200 in unison therewith. The spindle 120 is rotated by the rotary actuator, rotating the grinding wheel 1 about the rotational axis 2. The grinding fluid supply source connected to the grinding fluid supply channels 15 supplies the grinding fluid 126 to the area of the surface 201 of the workpiece 200 that faces along the rotational axis 2 the area of the grinding wheel 1 that lies radially inwardly of the grindstones 20. The grinding fluid supply source 125 also supplies the grinding fluid 126 to the area of the surface 201 of the workpiece 200 that faces along the rotational axis 2 the area of the grinding wheel 1 that lies radially outwardly of the grindstones 20. While thus supplying the grinding fluid 126 to the grindstones 20 and the workpiece 200, the grinding apparatus 100 moves the spindle 120 along the rotational axis 2 toward the chuck table 110 to bring the grindstones 20 of the grinding wheel 1 that is rotating about the rotational axis 2 into contact with the surface 201 of the workpiece 200 that is rotating about the rotational axis 112 and to press the grindstones 20 against the surface 201 of the workpiece 200, thereby grinding the surface 201 of the workpiece 200 with the grinding faces 25 of the grindstones 20.

Heretofore, the segments as the grindstones have had a thickness in the range of approximately 2 to 4 mm, a height in the range of approximately 4 to 5 mm, and an aspect ratio ranging from approximately 1 to 2.5 to safeguard against cracking while grinding workpieces. Therefore, the ductile material such as resin or metal contained in the workpieces are liable to be extended into burrs. According to the present embodiment, however, the grinding wheel 1 constructed as described above includes the grindstones 20 each shaped as a thin plate whose thickness 23 is 1 mm or smaller, arranged in an annular array along the circumferential directions. The grindstones 20 are fixed to the wheel base 10 so as to protrude from the free end 13 thereof along the thicknesswise directions of the wheel base 10, and have an aspect ratio in the range of 5 inclusive to 35 exclusive. Consequently, since the grindstones 20 are able to scrape off the ductile material such as resin or metal contained in the workpiece 200 with the grinding faces 25 each of a circumferentially slender shape having a thickness of 1 mm or smaller, the grinding apparatus 100 is advantageous in that it is more capable of preventing ductile materials contained in workpieces, such as resin or metal, from being extended into burrs than existing grinding wheels.

Further, since each of the grindstones 20 of the grinding wheel 1 according to the present embodiment includes an electroformed grindstone shaped as a rectangular plate and made up of abrasive grains that are secured together by an electroformed bond including nickel plating, the grindstones 20 are less likely to crack while grinding the workpiece 200 than the existing segments as the grindstones. Therefore, even though the grindstones 20 are thin, e.g., the thickness 23 of the grindstones 20 is 1 mm or smaller or 0.5 mm or smaller, and the grindstones 20 protrude to the height 24 where the aspect ratio is in the range of 5 inclusive to 35 exclusive, the grindstones 20 can grind the workpiece 200 without cracking. Inasmuch as the grinding wheel 1 according to the present embodiment has a high aspect ratio in the range of 5 inclusive to 35 exclusive, its service life is prolonged until the grindstones 20 become useless by being worn out while grinding the workpiece 200. If the aspect ratio of a grinding wheel is less than 5, its service life is shortened, and if it is 35 or larger, the grindstones tend to crack and be broken while grinding workpieces.

Further, the thickness 23 of each of the grindstones 20 of the grinding wheel 1 according to the present embodiment is 1 mm or smaller. Consequently, the grindstones 20 can easily be formed as electroformed grindstones each shaped as a rectangular plate and made up of abrasive grains that are secured together by an electroformed bond including nickel plating. In addition, as the grindstones 20 can easily be inserted into the annular slot 14 in the wheel base 10, the manufacturing cost and grinding cost of the grinding wheel 1 can be reduced.

In a case where the thickness 23 of each of the grindstones 20 of the grinding wheel 1 according to the present embodiment is thinner, i.e., 0.5 mm or smaller, the thickness 23 of each of the grinding faces 25 that are of a circumferentially slender shape is also thinner, i.e., 0.5 mm or smaller. The grindstones 20 are more effective to scrape off the ductile material such as resin or metal contained in the workpiece 200, and hence are more capable of preventing ductile materials contained in workpieces, such as resin or metal, from being extended into burrs than existing grindstones. In a case where the thickness 23 of each of the grindstones 20 of the grinding wheel 1 according to the present embodiment is thinner, i.e., 0.5 mm or smaller, the grindstones 20 can more easily be formed as electroformed grindstones each shaped as a rectangular plate and made up of abrasive grains that are secured together by an electroformed bond including nickel plating. In addition, as the grindstones 20 can more easily be inserted into the annular slot 14 in the wheel base 10, the manufacturing cost and grinding cost of the grinding wheel 1 can further be reduced.

Further, since each of the grindstones 20 of the grinding wheel 1 according to the present embodiment includes an electroformed grindstone shaped as a rectangular plate and made up of abrasive grains that are secured together by an electroformed bond including nickel plating, the grindstones 20 are of high thermal conductivity and hence can quickly dissipate the heat generated by grinding the workpiece 200, thereby preventing the ductile material such as resin or metal contained in the workpiece 200 from being extended into burrs and also preventing the ductile material from being deposited on the grindstones 20 and loading the grindstones 20.

The present invention is not limited to the above embodiment. Stated otherwise, various changes and modifications may be made in the embodiment without departing from the scope of the invention. For example, according to the present embodiment, the grinding wheel 1 is applied to an in-feed grinding method in which the grindstones 20 as they rotate about the rotational axis 2 grind the workpiece 200 while the workpiece 200 is rotating about its central axis, i.e., the rotational axis 112. However, the grinding wheel according to the present invention may be applied to a creep-feed grinding method in which the grindstones 20 as they rotate about the rotational axis 2 grind the workpiece 200 while not rotating about its central axis, i.e., the rotational axis 112, but moving radially toward the rotational axis 2.

The present invention is not limited to the details of the above described preferred embodiment. The scope of the invention is defined by the appended claims and all changes and modifications as fall within the equivalence of the scope of the claims are therefore to be embraced by the invention. 

What is claimed is:
 1. A grinding wheel for grinding a workpiece containing a ductile material, the grinding wheel comprising: an annular wheel base having a fixed end adapted to be fixed to a lower end of a spindle and having a free end adapted to face the workpiece to be ground; and a plurality of grindstones each shaped as a rectangular plate, disposed on the free end of the annular wheel base, and arrayed at predetermined intervals with respective longer sides disposed along circumferential directions of the wheel base, wherein each of the grindstones includes an electroformed grindstone shaped as a rectangular plate and made up of abrasive grains secured together by nickel plating, and has a thickness of 1 mm or smaller and a value ranging from 5 inclusive to 35 exclusive that is represented by a ratio of a height from the free end to the thickness.
 2. The grinding wheel according to claim 1, wherein the thickness of each of the rectangular, plate-shaped grindstones is 0.5 mm or smaller.
 3. The grinding wheel according to claim 1, wherein the workpiece contains resin as the ductile material on a surface thereof to be ground by the grinding wheel.
 4. The grinding wheel according to claim 1, wherein the workpiece contains metal as the ductile material on a surface thereof to be ground by the grinding wheel. 